In this day and age, send them an actual note in the mail (snail mail).
Had a friend that was in a real funk for a bit, I went to the store and bought 14 cards.
Some of the cards were blank, some "thinking of you" cards.
I printed the address with a different font for each of the 14 different envelopes.
Single line of text saying hello one day, long paragraph stating how much they meant in others.
No return email address on the envelopes - just a hand written smiley face.
Mailed one every day for 14 straight days.
The person still holds on to everyone of them.
For Easter one year, went to a craft store and bought a bunch of flat styrofoam eggs, glued them together in pairs with a "pocket" open at the top. Filled each one with a different gift certificates $5 ~ $20 to various local eateries/stores. My brothers now hate me - as I had shown my sisters and sisters in-law what i had done - and now they have higher expectations out of my brothers
Big in surprising a person in little ways frequently here.